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Once Email API documentation

Public developer documentation for automated email testing: authentication, quotas, errors, and safe-use rules.

Documentation is public. API keys are available only with an active Developer subscription and are managed in the account dashboard.
Authentication

Send Authorization: Bearer oe_live_… with every request. A key is shown once; keep it in a secrets manager and never place it in browser code, logs, or Git.

Authorization: Bearer oe_live_your_key
Typical workflow
  1. 1Create a temporary inbox and retain its inbox ID.
  2. 2Ask your test system to send mail to that address.
  3. 3Poll the message list with backoff; avoid rapid empty polling.
  4. 4Read the target message, complete assertions, then delete the inbox.

Status codes

400

Invalid request

401

Missing or invalid key

403

Plan or resource denied

404

Resource not found

429

Rate or monthly quota reached

5xx

Temporary service failure

Acceptable use

Use the API only on systems you are authorized to test. Spam, policy evasion, account abuse, monitoring other people’s communications, and long-term personal-data storage are prohibited. Message bodies and attachments do not enter account history.

The API is entering production readiness
This public contract is published first. Key creation and live calls will open only after payment webhooks, quotas, and regression gates pass.
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